1. Field of the Invention
The present invention relates to an apparatus for positioning a thin plate and, more specifically, to an apparatus for detecting a mark provided at a predetermined position on a thin plate placed on a stage and positioning the thin plate in place.
2. Description of the Related Art
During the production of a semiconductor device, a flip-chip system can be adopted wherein electrode terminals of a semiconductor element are directly placed on a circuit board for forming a semiconductor device package. To adopt the flip-chip system, it is necessary to provide bumps on the respective electrode terminals to be in contact and connected with predetermined locations on the circuit board.
One method for forming such bumps is illustrated in FIG. 5. According to the bump-formation system shown in FIG. 5, after a semiconductor element 10 has been placed on a table 200 adapted to be movable in the horizontal direction so that electrode terminals 12 thereof are directed upward (see FIG. 5(a)), a gold bump 14 having a pointed distal end is formed on the respective electrode terminal 12, 12, . . . (see FIG. 5(b)).
This gold bump 14 is formed on the electrode terminal 12 by using a bonding device 40 shown in FIG. 6. In the bonding device 40, a tip end of a gold wire 44 wound on a wire spool 42 is heated, after passing through a clamper 46 and a capillary 48, to form a ball-like end 49. Thereafter, the capillary 48 descends to pressingly bond the ball-like end 49 onto the electrode terminal 12. Then, the gold wire 44 is stretchingly severed by means of the clamper 46 to form the gold bump 14 having a pointed tip end.
Such gold bumps 14, 14, . . . having the pointed ends are then subjected to a flattening treatment to be converted into bumps 16, 16, . . . having flat ends (see FIG. 5(c)).
In the bonding device 40 shown in FIG. 6, the semiconductor element 10 placed on the table 200 is initially detected and located (fixed) at a predetermined position since it is necessary to form the ball-like ends 49 of the gold wire 44 exactly above the electrode terminals 12, 12, . . . of the semiconductor element 10.
The electrode terminals 12, 12, . . . of the semiconductor element 10 detected and located on the table 200 are formed at predetermined positions on one surface of the semiconductor element 10. For this purpose, the semiconductor element 10 is movable by, for example, a controller (not shown) for controlling a drive means such as a servo-motor (not shown) for moving the table 200 in the horizontal direction so that a selected electrode terminal 12 on which the gold bump 14 is to be formed is positioned exactly beneath the ball-like end 49 of the gold wire 44.
In the prior art, the detection and positioning of the semiconductor element 10 placed on the table 200 are carried out by a positioning device shown in FIG. 7.
The positioning device shown in FIG. 7 includes the table 200 movable in the horizontal direction and having a suction hole 204 formed in a central region of the table 200 and fluidly connected to a vacuum generating means 202 such as a vacuum pump, four pusher members 100 provided so that a front end face of each thereof abuts to the respective side of the rectangular semiconductor element 10 and is movable to be away from and closer to the semiconductor element 10 to slide the semiconductor element 10 in the predetermined direction, a camera 50 such as a CCD for detecting marks provided at a selected position on the surface of the semiconductor element 10 placed on the table 200, and an optical detection means having a controller 52 for controlling a drive means (not shown) such as a servo-motor for moving the camera 50 leftward and rightward.
In the above-mentioned positioning device, the camera 50 has a high magnification to accurately detect the marks formed on one surface of the semiconductor element 10, which means that the camera 50 has a smaller field of view 54. Accordingly, as shown in FIG. 7, it is impossible to cover all of one surface of the semiconductor element 10 by the field of view 54 of the camera 50 but only part of the semiconductor element 10 can be covered.
If the marks 18, 18 provided on one surface of the semiconductor element 10 placed on the table 200 are out of the field of view 54 of the camera 50, as shown in FIG. 8(a), the respective pusher members 100 move to cause the front end faces thereof to abut to the four sides of the rectangular semiconductor element 10, respectively, in four directions, to slide the semiconductor element 10 on the table 200 so that the mark 18 of the semiconductor element 10 is within the field of view 54 of the camera 50 located at a fixed position, as shown in FIG. 8(b). Thus, the position of the semiconductor element 10 is easily detectable.
Then, the vacuum generating means 202 such as a vacuum pump is driven to secure the semiconductor element 10 thus detected on the table 200 through the suction hole 204, after which the table moves to the subsequent process.
According to the positioning device shown in FIG. 7, the front end faces of the pusher members 100 abut to sides of the semiconductor element 10, respectively, to slide the latter, as shown in FIGS. 7 and 8(b). Therefore, a pushing force applied to the semiconductor element 10 by the two pusher members 100 opposite to each other is liable to bend the semiconductor element 10.
Recently, the semiconductor element 10 has been made thinner; for example, in an extreme case, a thickness is less than 150 xcexcm. Such a thin semiconductor element 10 may be bent due to a pushing force applied thereto while gripping the same between the front end faces of pusher members 100 disposed opposite to each other. In the semiconductor element 10 thus bent, even though the mark 18 is caught within the field of view of the camera 50, the position of the mark cannot be correctly detected.
Since the pusher members 100 must be in contact with and away from the semiconductor element 10 placed on the table 200, a predetermined gap is provided between the pusher member 100 and the table 200. There is a risk in that the thin semiconductor element 10 may slide into the gap 102.
Another prior art related to the present invention is disclosed in Japanese Examined Utility Model Publication No. 1-9168 wherein stopper portions are provided at opposite corners of a positioning stage, and position-restricting surfaces corresponding to outer sides of leads of a workpiece and contact surfaces to abut to the stopper portions are provided in pusher members, wherein the positional relationship between the position-restricting surfaces, the stopper portions and the contact surfaces is so selected that a sum of gaps between the position-restricting surfaces and the outer sides of the leads of the workpiece is equal to a predetermined value when the pusher members reach their foremost positions.
Also, in Japanese Unexamined Patent Publication No. 4-74443, a die-bonding device is disclosed, wherein a semiconductor chip is located on a positioning stage by a positioning member, then moves to a bonding position on a body to be bonded by means of a bonding head and is bonded onto the body. In this prior art, a protrusion is formed in a central region of the positioning stage, having a size smaller than the semiconductor chip. According to this device, any debris generated from the semiconductor chip during the positioning operation is not left on the stage surface on which the positioning of the semiconductor is carried out, whereby the positioning member can assuredly be brought into contact with the semiconductor chip every time to accurately locate the latter at a predetermined position.
Accordingly, an object of the present invention is to provide an apparatus for positioning a thin plate placed on a table, by slide means such as pusher members, which is free from a risk of bending the thin plate due to a pushing force applied thereto by the slide means while gripping the thin plate between front end faces of the slide means.
The inventors have studied to solve the above-mentioned problem in the prior art and found that it is possible to adjust a position of a thin plate without applying a large pushing force which can bend the thin plate by a slide means, by forming a stage on a table for placing the thin plate such as a semiconductor element. The stage has a flat placement surface for placing the thin plate thereon having such an area that when the thin plate is placed on the placement surface without projecting out therefrom, a mark formed on one surface of the thin plate is always caught within a field of view of a camera. The slide means is adapted to sliding the thin sheet placed on the placement surface of the stage to move the projected part of the thin plate into the area of the placement surface, so that a front end face of the slide means abuts to a lateral side of the stage.
According to the present invention, there is provided an apparatus for positioning a thin plate comprising: a stage having a flat placement surface on which said thin plate is mounted, said placement surface having a flat region which is slightly larger than, and completely covers, said thin plate, said placement surface also having at least one lateral side edge; optical detecting means arranged above said stage for detecting a mark provided on said thin plate, said optical detecting means having such a view that said mark can be caught by said view if said thin plate placed on said placement surface is within said flat region of the placement surface, but said mark cannot be caught by said view if said thin plate placed on said placement surface protrudes by a part thereof from said flat region of the placement surface; and adjusting means having a movable part which pushes said thin plate until it comes into contact with said lateral edge to move said thin plate so that said thin plate is brought within said flat region of the placement surface.
The flat placement surface is an upwardly protruded portion from a lower flat surface of a table and said movable part of the adjusting means is a pusher member which slidingly moves on said lower flat surface.
According to the present invention, if the thin plate slide means includes a pusher member having a front end face movable to be in contact with or move away from the lateral side of the stage on the table, the slide means becomes simple in structure.
If the means for fixing the thin plate at a predetermined position has a plurality of suction holes opened on the placement surface, the thin plate can be sucked by a plurality of positions whereby the deformation thereof is avoidable.
Further, the present invention is suitably applicable to a semiconductor element 150 xcexcm thick or less.
According to the apparatus for positioning the thin plate of the present invention, since the placement surface of the stage is flat and larger than the thin plate, there is no risk in that the thin plate is fixed between the front end faces of the slide means when the projected part of the thin plate placed on the placement surface of the stage formed on one side of the table slides into the area of the placement surface, whereby the bending of the thin plate due to the pushing force is avoidable.
Also, the placement surface has such an area that when the thin plate is placed on the placement surface without projecting outside thereof, the mark on the thin plate is always caught in the field of view of the camera. Thus, when the thin plate is completely placed on the placement surface of the stage by sliding the projected part of the thin plate into the placement surface by the slide means, the mark is also within the field of view of the camera, whereby the position of the thin plate is easily detectable.
Also, the thin plate thus position-detected is fixed on the stage by the fixing means to complete the positioning operation.